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Tire Rotational Speed

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Determining Tire Revolutions Per Second at 8 km/h (5 mph) - Using EVA 

Tire and wheel assembly rotational speed can be obtained through using the EL-38792-A  Electronic Vibration Analyzer (EVA) 2. Perform the following steps using the EL-38792-A  Electronic Vibration Analyzer (EVA) 2 to obtain the rotational speed at 8 km/h (5 mph). Use the Enter key to advance and the Exit key to backup.

  1. On the Main Menu screen, select Auto Mode.
  2. On the Suspected Source screen, select Vehicle Speed.
  3. On the Tire Info Source screen, select Manual Entry.
  4. On the Tire Width screen, enter the specific width of the tires.

    For example: For a P275/55R20 tire, enter 275.

  5. On the Aspect Ratio screen, enter the specific aspect ratio of the tires.

    For example: For a P275/55R20 tire, enter 0.55.

  6. On the Rim Diameter screen, enter the specific rim diameter size.

    For example: For a P275/55R20 tire, enter 20.0.

  7. On the Driveshaft Configuration screen, enter FWD, even if the vehicle is a rear wheel drive.
  8. The next screen will display the tire size just entered for confirmation.

    For example: 275 0.55 20.0 - Front Wheel Drive. If the tire size displayed is correct, press Enter.

  9. On the Vehicle Speed Units screen, press Enter, disregard mph or km/h.
  10. Press the Exit key several times slowly while watching the backwards progression of the screens. Stop at the Tire Info Source screen.
  11. On the Tire Info Source screen, select RPS at 5 mph.
  12. The next screen will display the revolutions per second (RPS) at 8 km/h (5 mph) for that specific tire size.

    For example: The P275/55R20 will display 0.90 RPS.

Calculating Tire Revolutions Per Second at 8 km/h (5 mph) - Without EVA 

If the EL-38792-A  Electronic Vibration Analyzer (EVA) 2 is not available, the tire and wheel assembly rotational speed can be calculated approximately by performing the following steps.

  1. Convert the rim diameter size from inches to centimeters.

    For example: For a P275/55R20 tire, the rim diameter of 20 in X 2.54 converts to 50.80 cm.

  2. Calculate the radius of the rim by dividing the rim diameter by 2.

    For example: For a P275/55R20 tire, the rim diameter of 20 in converted to 50.80 cm divided by 2 = rim radius 25.40 cm.

  3. Calculate the approximate tire sidewall height by multiplying the specific tire tread width by the aspect ratio, then reduce 7 percent from the amount by multiplying by 93 percent to approximate load on the tire reducing the sidewall height.

    For example: For a P275/55R20 tire, tread width 275 mm X aspect ratio as a decimal 0.55 = 151 mm X 0.93 = approximate sidewall height 140.43 mm.

  4. Convert the calculated approximate tire sidewall height from millimeters to centimeters.

    For example: For a P275/55R20 tire, approximate sidewall height 140.43 mm converts to 14.04 cm.

  5. Calculate the approximate tire and wheel assembly radius by adding the rim radius and approximate sidewall height, both in cm.

    For example: For a P275/55R20 tire, rim radius 25.40 cm + 14.04 cm = approximate tire and wheel assembly radius 39.44 cm.

  6. Calculate the approximate circumference of the tire and wheel assembly by multiplying 2 X pi, or 6.283185 X the approximate tire and wheel assembly radius.

    For example: For a P275/55R20 tire, 6.283185 X approximate tire and wheel assembly radius 39.44 cm = approximate tire and wheel assembly circumference 247.809 cm.

  7. Calculate the approximate revolutions per kilometer by dividing the number of cm in 1 km, 100, 000 cm by the approximate tire and wheel assembly circumference.

    For example: For a P275/55R20 tire, 100, 000 cm divided by approximate tire and wheel assembly circumference 247.809 cm = approximate revolutions per kilometer 403.537.

  8. Calculate the approximate revolutions per second (RPS), or Hz, by dividing the approximate revolutions per kilometer by the number of seconds to travel 1 km at a speed of 8 km per hour, 450 seconds.

    For example: For a P275/55R20 tire, approximate revolutions per kilometer 403.537 divided by the number of seconds to travel 1 km at a speed of 8 km per hour, 450 seconds = approximate RPS, or Hz 0.897 rounded to 0.90.

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